gcc -g1 does not do what the docs say?

[Alexey Neyman <alexey dot neyman at gmail dot com>]

Hi all,

The -g1 option is described in the GCC manual as follows:

"Request debugging information and also use level to specify how much 
information. The default level is 2.
...
Level 1 produces minimal information, enough for making backtraces in 
parts of the program that you don’t plan to debug. This includes 
descriptions of functions and external variables, and line number 
tables, but no information about local variables."

From that description, I assumed that variables with external linkage 
will have a debugging information present. I tried using -g1 option with 
DWARF format, using a simple file that has just one line:

int foo;

When compiled with `gcc -c -O2 -gdwarf-4 -g1`, it does not produce the 
Debugging Information Entry (DIE) for this variable, despite that 
variable having an external linkage. It does produce a DIE for it with 
the default debugging level (-g2). I tried various versions of GCC, from 
7.1.0 to 9.2.0, all behave in the same way. I also tried adding an 
__attribute__((externally_visible)) to that variable, but still got no 
DIE is generated for it.

Am I missing something? Or is it a bug in GCC?

Here is an example using GCC 9.2 that comes with Ubuntu 19.10:

aneyman@supox:/tmp$ cat foo.c
int foo __attribute__((externally_visible));
aneyman@supox:/tmp$ gcc -c -O2 -gdwarf -g1 foo.c
aneyman@supox:/tmp$ readelf -wi foo.o
aneyman@supox:/tmp$ gcc -c -O2 -gdwarf -g2 foo.c
aneyman@supox:/tmp$ readelf -wi foo.o
...
<1><1d>: Abbrev Number: 2 (DW_TAG_variable)
    <1e>   DW_AT_name        : foo

Regards,
Alexey.